The three main models (ECM. GFS, UKMO) now seemed to have firmed up on
the track of next week's depression, bringing it southwards just to our
west. The ECM operational run introduces a new feature, moving the Low
to our east by next weekend (i.e. 20th and 21st) and so introducing a
flow from a northerly quarter over the UK.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

In article ,
John Hall writes:
The three main models (ECM. GFS, UKMO) now seemed to have firmed up on
the track of next week's depression, bringing it southwards just to our
west. The ECM operational run introduces a new feature, moving the Low
to our east by next weekend (i.e. 20th and 21st) and so introducing a
flow from a northerly quarter over the UK.

The 18Z GFS operational run seems pretty much identical out to T+120
hours, which is as far as it's got at the moment. It looks as though
there could be an awful lot of precipitation over central southern
England and the east Midlands between about noon on Tuesday and noon on
Wednesday, as there's a band of heavy rain or snow that seems to hardly
move. So if there isn't very deep snow then there could well be
flooding.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

On 12 Feb, 22:14, John Hall wrote:
In article ,
*John Hall writes:

The three main models (ECM. GFS, UKMO) now seemed to have firmed up on
the track of next week's depression, bringing it southwards just to our
west. The ECM operational run introduces a new feature, moving the Low
to our east by next weekend (i.e. 20th and 21st) and so introducing a
flow from a northerly quarter over the UK.

The 18Z GFS operational run seems pretty much identical out to T+120
hours, which is as far as it's got at the moment. It looks as though
there could be an awful lot of precipitation over central southern
England and the east Midlands between about noon on Tuesday and noon on
Wednesday, as there's a band of heavy rain or snow that seems to hardly
move. So if there isn't very deep snow then there could well be
flooding.
--
John Hall
* * * * * *"Acting is merely the art of keeping a large group of people
* * * * * * from coughing."
* * * * * * * * * * * * * * * Sir Ralph Richardson (1902-83)

GFS 12/02/2010 18Z +102
http://www2.wetter3.de/Schnitte/1_102_L_0_0_B_34_71.gif
http://www.wzkarten3.de/pics/Rmgfs1023.gif

The first chart shows a cross section of the atmosphere running along
the 0 Longitude line, so London's at 51N. Looks like it's going to be
mainly rain? Very marginal, but gut feeling tells me it's going to be
mostly rain in Southern England. Let's hope my gut is wrong!

In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

"John Hall" wrote in message
...
In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.
The current T+72 FAX (DT 13th 12Z) cf old T+84 FAX is interesting. Look how
much further south the 528 line is on 12Z run. Only about 50 miles but it
can make all the difference.
If this trend continues then we have "snowmageddon" for the south :-)

Will
--

"Will Hand" wrote in message
...

"John Hall" wrote in message
...
In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.
The current T+72 FAX (DT 13th 12Z) cf old T+84 FAX is interesting. Look
how much further south the 528 line is on 12Z run. Only about 50 miles but
it can make all the difference.
If this trend continues then we have "snowmageddon" for the south :-)

Will
--

12Z ECM 13th (just coming in) is even colder - ooh er!
My forecast stands, no point in changing it.

Will
--

In article ,
Will Hand writes:

"John Hall" wrote in message news:$7iKTzBvlu
...
In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.

But the worded forecast is timed at 15:04, when the 12Z GFS wouldn't
have been available.

The current T+72 FAX (DT 13th 12Z) cf old T+84 FAX is interesting. Look
how much further south the 528 line is on 12Z run. Only about 50 miles
but it can make all the difference.
If this trend continues then we have "snowmageddon" for the south :-)


--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

"John Hall" wrote in message
...
In article ,
Will Hand writes:

"John Hall" wrote in message news:$7iKTzBvlu
...
In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.

But the worded forecast is timed at 15:04, when the 12Z GFS wouldn't
have been available.


12Z UKMO was though internally!

The current T+72 FAX (DT 13th 12Z) cf old T+84 FAX is interesting. Look
how much further south the 528 line is on 12Z run. Only about 50 miles
but it can make all the difference.
If this trend continues then we have "snowmageddon" for the south :-)


--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

In article ,
Will Hand writes:

"John Hall" wrote in message news:NoB2nrKihv
...
In article ,
Will Hand writes:

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.

But the worded forecast is timed at 15:04, when the 12Z GFS wouldn't
have been available.


12Z UKMO was though internally!

Ah, I see. I thought it might be available internally a bit earlier than
outsiders see it, but not a whole three hours earlier than it appears on
Wetterzentrale.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)